The subject matter of this disclosure relates generally to power converters, and more particularly to power converter topologies based on H-bridges that are coupled to one or more multi-phase electromagnetic energy conversion devices (EMECDs), including without limitation, multi-phase transformers with open windings and/or electric machines with open windings, to provide a regenerative or partial regenerative power converter.
Power converter cell topologies associated with variable frequency drive (VFD) applications continue to receive attention. New power converter cell topologies are continually being introduced. Some known power converter cell topologies have employed H-bridge converters and/or H-bridge inverters.
Some of the foregoing power cells, when connected to a load, such as a motor, can provide power from an input source to a motor when operating in the motoring mode. Such a power cell may sometimes be referred to as a unidirectional or two-quadrant (2Q) cell. This is because when the four quadrants of speed and torque are considered, the operating characteristics of the cell are such that it operates in either the quadrant where both speed and torque are positive (first quadrant) or the quadrant where both speed and torque are negative (third quadrant).
When motor speed need to be reduced however, power from the motor needs to be absorbed by the power converter cell. This mode of operation is generally referred to as the regeneration mode. In such operating modes, regenerative or four-quadrant cells are required.
A regenerative converter may include a three level output power conversion stage. The output power stage generally includes electrical switches such as IGBTs (Insulated Gate Bipolar Transistors). Other useful switches include GTOs (Gate Turn Off Thyristors), IGCTs (Integrated Gate Commutated Thyristors), IEGTs (Injection Enhanced Gate Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The switches may be paired with anti-parallel freewheeling diodes to accommodate, for example, inductive motor load currents. A controller is generally used for controlling each of the switches. The controller may comprise, for example, a computer and/or a digital signal processor.
Known regenerative power converter topologies comprising H-bridges continue to struggle with size, cost and reliability constraints due to the high number of active switches required to provide a workable topology. In view of the foregoing, there is a need to provide a regenerative power converter cell structure that requires fewer active switches to provide a workable topology having fewer components, higher reliability, less cost, and that has a smaller physical size than known regenerative power converter cell topologies.